CHAPTER X.
The Products of Vegetation—Importance ofChemicalquality as well as quantity of Produce—Influence of different Manures on the quantity and quality of the Crop—Influence of the time of Cutting—Absolute quantity of Food yielded by different Crops—Principles on which the Feeding of Animals depends—Theoretical and experimental value of different kinds of Food for Feeding Stock—Concluding Observations.
The Products of Vegetation—Importance ofChemicalquality as well as quantity of Produce—Influence of different Manures on the quantity and quality of the Crop—Influence of the time of Cutting—Absolute quantity of Food yielded by different Crops—Principles on which the Feeding of Animals depends—Theoretical and experimental value of different kinds of Food for Feeding Stock—Concluding Observations.
The first object of the practical farmer is, to reap from his land the largest possible return of the most valuable crops, without permanently exhausting the soil. With this view he adopts one or other of the methods of treatment above adverted to, by which either the physical condition or the chemical constitution of the soil is altered for the better. It may be useful to shew how very much both the quantity and the quality of a crop is dependent upon the mode in which it iscultivated and reaped, and how much control, therefore, the skilful agriculturist really possesses over the ordinary productions of nature.
Every one knows that some soils naturally produce much larger returns of wheat, oats, and barley than others do, and that the same soil will produce more or less according to the mode in which the land has been prepared by manure, or otherwise, for the reception of the seed. The following table shews the effect produced upon the quantity of the crop byequal quantitiesof different manures applied to thesame soil, sown with an equal quantity of the same seed.
It is probable that on different soils the returns obtained by the use of these several manures may not be always in the same order, yet, generally speaking, it will always be found that blood, night-soil, and sheep, horse, and pigeon’s dung, are among the most enriching manures that can be employed.
We have already seen a theoretical reason for believing that night-soil should be among the most enriching manures, and the result of actual trial here shews that it is one of the most practically valuable which the farmer can employ.
Two other facts will strike the practical man on looking at the above table.
1. That exclusive of blood, sheep’s dung gave the greatest increase in the barley crop. The favourite Norfolk system of eating off turnips with sheep previous to barley, besides other benefits which are known to attend the practice, may owe part of its acknowledged utility to this powerful action of sheep’s dung upon the barley crop.
2. The action of cow dung upon oats is equally striking, and the large return obtained by the use of vegetable manure alone—thirteen fold—may perhaps explain why in poorly farmed districts oats should be a favourite and comparatively profitable crop, and why they may becultivated with a certain degree of success on lands to which no rich manure is ever added.
But the quality of the grain also, as well as its quantity, is materially affected by the kind of manure by which its growth is assisted. The apparent quality of wheat and oats is very various; but in samples apparently equal in quality, important chemical differences may exist, by which it is believed that the nourishing properties of the grain are materially affected.
It has been stated in a previous chapter (p. 43), that when flour is made into dough, and this dough is washed upon a linen cloth with water as long as the latter passes through milky,—the flour is separated intostarch, which subsides from the water, andgluten, which remains behind. The quantity of gluten thus left varies more or less with almost every sample of flour, and the nutritive properties of each sample are supposed to depend very much upon the quantity of gluten it contains. So far it seems to be pretty well ascertained, that those varieties of grain which contain thelargest amount of gluten yield also the greatest return of flour, and the heaviest weight of bread.
The weight of gluten contained in 100 lbs. of dry wheat has been found to vary from 8 to 34 lbs., and this proportion is affected in a very remarkable manner by the kind of manure which has been applied to the land. Thus the proportions of starch and gluten in 100 lbs. of the grain of the same wheat, grown on the same land, differently manured, was as follows:—
Potato-flour, which consists entirely of starch, makes a fine light bread, easily raised. Wheaten-flour, which contains little gluten, approaches in this respect to potato-flour. When the quantity of gluten is large, greater care is required to make a good light bread; but the bread from such flour is generally found to be more nutritive in its quality. A dough peculiarly rich in gluten is required for the manufacture of macaroni and vermicelli; such is said to be the flour naturally produced in southern Italy. By the above table it appears,that the use of richer animal, or poorer vegetable manures, would enable the farmer to raise, at his pleasure, either a rich macaroni wheat, or one poor in gluten suited for the makers of fancy bread.
An equally striking effect is not produced upon other kinds of grain by varying the manure. Thus the proportions of starch and gluten in the dry grain of barley and oats, differently manured, were found to be as follows:—
Though a variation in the proportion of gluten can be observed in both of these kinds of grain, according as one or other of the above kinds of manure was employed, yet neither the average quantity of gluten present in them, nor the variations to which the quantity is liable, are at all equal in amount to what are observed in the case of wheat.
The malting of barley is known to be affected by a variety of circumstances. It should be so uniform in ripeness as to sprout uniformly, so that no part of it should be beginning to shoot when the rest has already germinated sufficiently for the maker’s purpose. On this perfect sprouting of thewholedepends in some degree the swelling of the malt, which is of considerable consequence to the manufacturer.
But themeltingquality of the grain, which is of more consequence to the brewer and distiller, is modified chiefly by the proportion of gluten which the barley contains. That which contains the least gluten, and therefore the most starch, will melt the most easily and the most completely, and will yield the strongest beer or spirit from the same quantity of grain. Hence the preference given by the brewer to the malt of particular districts, even where the sample appears otherwise inferior. Thus the brewers on the sea-board of the county of Durham will not purchase the barley of their own neighbourhood, while Norfolk grain can be had at a moderate increase of price. But that which refuses to melt well in the hands of the brewer, will cause pigs and other stock to thrive well in the hands of the feeder, and this is the chief outlet for the barley which the brewer and distiller reject.
So far as a practical deduction can be drawn from the effects of different manures on the proportion of gluten in barley, it would appear that the larger the quantity of cow dung contained in the manure applied to barley land—in other words,the greater the numbers of stock folded about the farm-yard, the more likely is the barley to be such as will bring a high price from the brewer.
The folding ofsheepproduces a larger return (p. 206), from the barley crop—while the folding ofcattlegives grain of a better malting quality.
The period at which hay is cut, or corn reaped, materially affects the quantity (by weight) and the quality of the produce. It is commonly known that when radishes are left too long in the ground they become hard and woody—that the soft turnippy stem of the young cabbage undergoes a similar change as the plant grows old,—and that the artichoke becomes tough and uneatable if left too long uncut. The same natural change goes on in the grasses which are cut for hay.
In the blades and stems of the young grasses there is much sugar,which, as they grow up, is gradually changed, first into starch, and then into woody fibre (pages 44 and 45.) The more completely the latter change is effected—that is, the riper the plant becomes—the less sugar and starch, both readily soluble substances, they contain. And though it has been ascertained that woody fibre is not wholly indigestible, but that the cow, for example, can appropriate a portion of it for food as it passes through her stomach; yet the reader will readily imagine, that those parts of the food which dissolve most easily, are also likely—other things being equal—to be most nourishing to the animal.
It is ascertained, also, that the weight of hay or straw reaped, is actually less when allowed to become fully ripe; and therefore, by cutting soon after the plant has attained its greatest height, a larger quantity, as well as a better quality of hay, will be obtained, while the land also will be less exhausted.
The same remarks apply to crops of corn,—both to the straw and to the grain they yield. Therawerthe crop is cut, the heavier and more nourishing the straw. Within three weeks of being fully ripe, the straw begins to diminish in weight, and the longer it remains uncut after that time, the lighter it becomes and the less nourishing.
On the other hand, the ear which is sweet and milky a month before it is ripe, gradually consolidates, the sugar changing into starch, and the milk thickening into the gluten and thealbumen[22]of the flour. As soon as this change is nearly completed, or about a fortnight before ripening, the grain contains the largest proportion of starch and gluten; if reaped at this time, the bushel will be heavier, and will yield the largest quantity of fine flour and the least bran.
At this period the grain has a thin skin, and hence the small quantity of bran. But if the crop be still left uncut, the next natural step in the ripening process is, to cover the grain with a better protection, a thicker skin. A portion of the starch of the grain is changed into woody fibre,—precisely as in the ripening of hay, of the soft shoots of the dog-rose, and of the roots of the common radish. By this change, therefore, the quantity of starch is lessened and the weight of husk increased; hence the diminished yield of flour, and the increased produce of bran.
Theory and experience, therefore, indicate about a fortnight before full ripening as the most proper time for cutting corn. The skin is then thinner, the grain fuller, the bushel heavier, the yield of flour greater, the quantity of bran less; while, at the same time, the straw is heavier, and contains more soluble matter than when it is left uncut until it is considered to be fully ripe.[23]
The quantity of food capable of yielding nourishment to man, which can be grown from an acre of land of average quality, depends very much upon the kind of crop we raise.
In seeds, when fully ripe, little sugar or gum is generally present, and it is chiefly by the amount of starch and gluten they contain, that their nutritive power is to be estimated. In bulbs, such as the turnip and potato, sugar and gum are almost always present in considerablequantity in the state in which these roots are consumed, and this is especially the case with the turnip. These substances, therefore, must be included among the nutritive ingredients of such kinds of food.
If we suppose an acre of land to yield the following quantities of the usually cultivated crops, namely—
The weight of dry starch, gluten, sugar, and gum, reaped in each crop, will be represented very nearly by the following numbers:—
If it be granted that the crops above stated are fair average returns from the same quality of land—that the acre, for example, which produces 25 bushels of wheat, will also produce 10 tons of potatoes, and so on—then it appears that the land which, by cropping with wheat, would yield a given weight ofstarch, would, when cropped with barley or oats, yield one-half more, with Indian corn or potatoes about three times as much, and with turnips five times the same quantity. In other words, the piece of ground which, when sown with wheat, will maintain one man, would support one and a half if sown with barley or oats, three with Indian corn or potatoes, and five withturnips—in so far as the nutritive power of these crops depends upon the starch and sugar they contain.
Again, if we compare the relative quantities of gluten, we see that wheat, beans, and Indian corn yield, from the same breadth of land, nearly an equal quantity of this kind of nourishment—potatoes one-third less, and barley and oats only one-third of the quantity—while turnips yield four times as much as either wheat, beans, or Indian corn.
On whichever of these two substances, therefore, the starch or the gluten, we consider the nutritive property of the above kind of food todepend, it appears that the turnip is by far the most nutritive crop we can raise. It is by no means the most nutritive weight for weight, but the largeness of the crop (25 tons) affords us from the same field a much greater weight of food than can be reaped in the form of any of the other crops here mentioned.
In this the practical farmer will see the peculiar adaptation of the turnip husbandry to the rearing and fattening of stock. Could the turnip be made an agreeable article of general human consumption, the produce of the land might be made to sustain a much larger population than under any other of the above kinds of cropping.
The relative nourishing power or value as food of different vegetable substances, is supposed by some to depend entirely upon the relative proportions of gluten they contain. According to this view, the pea and the bean are much more nourishing, weight for weight, even than wheat, and this latter grain, than any of the other substances mentioned in the above table. Thus, 56 lbs. of beans would afford as much sustenance to an animal as 67 of pease, 100 of wheat-flour, or 177of rice.
In order to understand the value of this opinion, it will be proper to consider the several purposes which the food is destined to serve in the animal economy—what the animal must derive from its food to maintain its existing condition, or to admit of a healthy increase of bulk.
The food of plants we have seen to consist essentially of two kinds, theorganicand theinorganic, both of which we have insisted upon as equally necessary to the living vegetable—equally indispensable to its healthy growth. A brief glance at the purposes served by plants in the feeding of animals, will not only confirm this view, but will also throw some additional light upon thekindof inorganic food which the plants must be able to procure, in order that they may be fitted to fulfil their assigned purpose in the economy of nature.
Man, and all domestic animals, may be supported, may even be fattened, upon vegetable food alone: vegetables, therefore, must contain all the substances which are necessary to build up the several parts of animal bodies, and to supply the waste attendant upon the performance of thenecessary functions of animal life. Let us consider what these substances are, and in what quantities they must be supplied to the human body.
1.The food must supply carbon for respiration.
A man of sedentary habits, or whose occupation requires little bodily exertion, may respire about 5 ounces of carbon in twenty-four hours—one who takes moderate exercise, about 8 ounces—and one who has to undergo violent bodily exertion, from 12 to 15 ounces.
If we take the mean quantity of 8 ounces, then to supply this alone, a man must eat 18 ounces of starch or sugar every day. If he take it in the form of wheaten bread, he will require 1¾ lbs. of bread, if in the form of potatoes, about 7½ lbs. of raw potatoes, to supply the waste caused by his respiratory organs alone.
When the habits are sedentary, 5 lbs. of potatoes may be sufficient, when violent and continued exercise is taken, 12 to 15 lbs. may be too little. At the same time, it must be observed, that where the supply is less, the quantity of carbonic acid given off will either be less also, or the deficiency will be supplied at the expense of the body itself. In either case the strength will be impaired, and fresh food will be required to recruit the exhausted frame.
2.The food must repair the daily waste of the muscular parts of the body.
When the body is full grown, a portion from every part of it is daily abstracted by natural processes, and rejected either in the perspiration or in the solid and fluid excrements. This portion must be supplied by the food, or the strength will diminish—the frame will gradually waste away.
The muscles of animals, of which lean beef and mutton are examples, are generally coloured by blood, but when well washed with water, they become quite white, and, with the exception of a little fat, are found to consist of a white fibrous substance, to which the name offibrinhas been given by chemists. The clot of the blood consists of the same substance; while skin, hair, horn, and the organic part of the bones, are composed of varieties ofgelatine. This latter substance is familiarly known in the form ofglue, and though it differs in its sensible properties, it is remarkably analogous tofibrinin its elementary constitution, as both of these substances are to the white of the egg (albumen), to the curd of milk (casein), and to theglutenof flour. They all contain nitrogen, and all consist of the four elementary bodies (organic elements), very nearly in the following proportions:—
They all contain, likewise, a small proportion of sulphur and of phosphorus.
The quantity of one or other of these removed from the body in 24 hours, either in the perspiration or in the excretions, amounts toabout five ounces, containing 350 grains of nitrogen, and this waste at least must be made up by the gluten or fibrin of the food.
In the 1¾ lb. of wheaten bread we have supposed to be eaten to supply carbon for respiration, there will be contained also about 3 ounces of gluten. Let the other 2 ounces be made up in beef, of which half a pound contains 2 ounces of dry fibrin, and we have
If, again, the 7½ lbs. of potatoes be eaten, then in these are contained about 2½ ounces of gluten or albumen, so that there remain 2½ ounces to be supplied by beef, eggs, milk, or cheese.
The reader, therefore, will understand why a diet which will keep up the human strength is easiest compounded of a mixture of vegetable and animal food. It is not merely that such a mixture is more agreeable to the palate, or even that it is absolutely necessary,—for, as already observed, the strength may be fully maintained by vegetable food alone;—it is, that without animal food in one form or another, so large a bulk of vegetable food must be consumed in order to supply the requisite quantity of nitrogen in the form of gluten. Of ordinary wheaten bread alone, about 3 lbs. daily must be eaten to supply the nitrogen,[24]and there would then be a considerable waste of carbon in the form of starch, by which the stomach would be overloaded, and which, not being worked up by respiration, would pass off in the excretions. The wants of the body would be equally supplied, and with more ease, by 1¾ lbs. of bread and 4 ounces of cheese.
Of rice, again, no less than 4 lbs. daily would be required to impart to the system the required proportion of gluten; and it is a familiar observation of those who have been in India and other countries, where rice is the usual food of the people, that the degree to which the natives distend, and apparently overload their stomachs with this grain, is quite extraordinary.
The stomachs and other digestive apparatus of our domestic animals are of larger dimensions, and they are able, therefore, to contain with ease as much vegetable food, of almost any wholesome variety, as will supply them with the quantity of nitrogen they may require. Yet every feeder of stock knows that the addition of a small portion of oil-cake, a substance rich in nitrogen, will not only fatten an animal more speedily, but will also save a largebulkof other kinds of food.
3. But the blood and other fluids of the body contain muchsalinematter of various kinds, sulphates, muriates, phosphates, and other saline compounds of potash, soda, lime, and magnesia. All these have their special functions to perform in the animal economy, and of each of them an undetermined quantity daily escapes from the body in the perspiration, in the urine, or in the solid excretions. This quantity, therefore, must be daily restored by the food.
No precise experiments have yet been made with the view of determining how much saline matter is daily excreted from the body of a healthy man, or in what proportions the different inorganic substances are present in it; but it is satisfactorily ascertained, that without a certainsufficientsupply, the animal will languish and decay, even though carbon and nitrogen in the form of starch and gluten be abundantly given to it. It is a wise and beautiful provision of nature, therefore, that plants are so organized as to refuse to grow in a soil from which they cannot readily obtain a supply of soluble inorganic food, since that saline matter which ministers first to their own wants is afterwards surrendered by them to the animals they are destined to feed.
Thus the dead earth and the living animal are but parts of the same system,—links in the same endless chain of natural existences,—the plant is the connecting bond by which they are tied together on the one hand,—the decaying animal matter which returns to the soil, connects them on the other.
4. The solid bones of the animal are supplied from the same original source,—the vegetable food on which they live. The bones of the cowcontain 55 per cent. of phosphate of lime, of the sheep 70, of the horse 67, of the calf 54, and of the pig 52 lbs., in every hundred of dry bone. All this must come from the vegetable food. Of the bone-earth also, a portion,—perhaps a variable portion,—is every day rejected from the animal; the food, therefore, must contain a daily supply, or that which passes off will be taken from the substance of the bones, and the animal will become feeble.
It is kindly provided by nature, that a certain proportion of this ingredient of bones is always associated with the gluten of plants in its various forms,—with the fibrin of animal muscle and with the curd of milk. Hence, man, in using any of these latter along with his vegetable food, obtains from them, with comparative ease, the quantity of the earth of bones which is necessary to keep his system in repair; while those animals which live upon vegetables alone, extract all they require along with the gluten of the plants on which they feed.
The provision is very beautiful by which the young animal,—the muscle and bones of which are rapidly growing,—is supplied with a larger portion of nitrogenous food and of bone-earth, than are necessary to maintain the healthy condition of the full grown animal. The milk ofthe mother is the natural food from which its supplies are drawn. The sugar of the milk supplies the comparatively small quantity of carbon necessary for the respiration of the young animal; as it gets older, the calf or young lamb crops green food for itself to supply an additional portion. The curd of the milk (casein) yields the materials of the growing muscles, and of the animal part of the bones,—while dissolved along with the curd in the liquid milk is the phosphate of lime, of which the earthy part of the bones is to be built up. A glance at the constitution of milk will shew us how copious the supply of all these substances is,—how beautifully the constitution of the mother’s milk is adapted to the wants of her infant offspring. Cow’s milk consists in 1000 parts by weight of—
The quality of the milk, and, consequently, the proportions of theseveral constituents above mentioned, vary with the breed of the cow,—with the food on which it is supported,—with the time that has elapsed since the period of calving,—with its age, its state of health, and with the warmth of the weather;[25]but in all cases this fluid contains the same substances, though in different quantities.
Milk of the quality above analyzed contains, in every ten gallons, 4½ lbs. of casein, equal to the formation of 18 lbs. of ordinary muscle, and 3½ ounces of phosphate of lime (bone-earth), equal to the production of 7 ounces of dry bone. But from the casein have to be formed the skin, the hair, the horn, the hoof, &c. as well as the muscle, and in all these is contained also a minute portion of the bone-earth. A portion of all the ingredients of the milk likewise passes off in the ordinary excretions, and yet every one knows how rapidly young animals thrive, when allowed to consume the whole of the milk which nature has provided as their most suitable nourishment.
And whence does the mother derive all this gluten and bone-earth, by which she can not only repair the natural waste of her own full grownbody, but from which she can spare enough also to yield so large a supply of nourishing milk? She must extract them from the vegetables on which she lives, and they again from the soil.
The quantity of solid matter thus yielded by the cow in her milk is really very large, if we look at the produce of an entire year. If the average yield of milk be 3000 quarts, or 750 gallons in a year—every 10 gallons of which contain bone-earth enough to form about 7 ounces of dry bone—then the milking of the cow alone exhausts her of the earthy ingredients of 33 lbs. of dry bone. And this she draws necessarily from the soil!
If this milk be consumed on the spot, then all returns again to the soil in the annual manuring of the land. Let it be carried for sale to a distance, or let it be converted into cheese and butter, and in this form exported, there will then be a yearly drain upon the land of the materials of bones, from this cause alone, equal to 30 lbs. of bone-dust. After the lapse of centuries, it is conceivable that old pasture lands in cheese and dairy countries should become poor in the materials of bones—and that in such districts, as now in Cheshire, the application of bone-dust should entirely alter the character of the grasses, and renovate the old pastures.
Thus, as was stated at the commencement of the present section the study of the nature, and functions of the food of animals throws additional light upon the nature also and final uses of the food of plants. It even teaches us what to look for in the soil—what a fertile soilmustcontain that it may grow nourishing food—what we must add to the soil when chemical analysis fails to detect its actual presence, or when the food it produces is unable to supply all that the animal requires.
The principles above explained, therefore, shew that the value of any vegetable production, considered as thesolefood of an animal, is not to be judged of—cannot, in short, be accurately determined—by the amount it may contain of anyoneof those substances,allof which together are necessary to build up the growing body of the young animal, and to repair the natural waste of such as have attained to their fullest size.
Hence the failure of the attempts that have been made to support the lives of animals by feeding them upon pure starch or sugar alone. These substances would supply carbon for respiration, but all the natural waste of nitrogen, of saline matter, and of earthy phosphates, must have been drawn from the existing solids and fluids of their livingbodies. The animals in consequence pined away, and sooner or later died.
Some have expressed surprise that animals have refused to thrive, and have ultimately died, when fed upon animal jelly or gelatine (from bones) alone, nourishing though that substanceas part of the foodundoubtedly is. When given in sufficient quantity, gelatine might indeed supply carbon enough for respiration, with a great waste of nitrogen, but it is deficient in the saline ingredients which a naturally nourishing food contains.
Even on the natural mixture of starch and gluten in fine white bread, dogs have been unable to live beyond 50 days, though others fed on household bread, containing a portion of the bran—in which earthy matter more largely resides—continued to thrive long after. It is immaterial whether the general quantity of thewholefood be reduced too low, or whetheroneof its necessary ingredients only be too much diminished or entirely withdrawn. In either case, the effect will be the same—the animal will pine away, and sooner or later die.
From what has been stated in the preceding section, it appears, that, for various reasons, different kinds of food are not equally nourishing. This fact is of great importance, not only in the preparation of human food, but also in the feeding of stock. It has, therefore, been made the subject of experiment by many practical agriculturists, with the following general results.
If common hay be taken as the standard of comparison, then to yield the same amount of nourishment with 10 lbs. of hay, a weight of the other kinds of food must be given, which is represented by the number opposite to each in the following table:—
It is found in practice, as the above table shews, that twenty stones of potatoes or three of oil-cake will nourish an animal as much as ten stones of hay, and five stones of oats as much as either. Something, however, will depend upon the quality of each kind of food, and upon the age and constitution of the animal. The skilful feeder of stock knows also the value of a change of food, or of a mixture of the different kinds of vegetable food he may have at his command.
The nutritive value of different kinds of food has also been represented theoretically, by supposing it to be very nearly in proportion to the quantity of nitrogen, or of gluten, which vegetables contain. Though this cannot be considered as a correct principle, yet as the ordinary kind of food on which stock is fed contains in general an ample supply of carbon for respiration, with a comparatively small proportion of nitrogen, these theoretical determinations are by no means without their value, and they approach in many cases very closely to the practical values above given, as deduced from actual trial. Thus, assuming that 10 lbs. of hay yield a certain amount of nourishment, then of the other vegetable substances it will benecessary, according to theory, to give the following quantities, in order to produce the same effect:
If the feeder be careful to supply his stock with a mixture or occasional change of food, he may very safely regulate the quantity of any one he ought to substitute for a given weight of any of the others, by the numbers in the above tables—since the theoretical and practical results do not in general very greatly differ.
As has been already stated, it is not strictly correct that this or that kind of vegetable is more fitted to sustain animal life, simply because of the larger proportion of nitrogen it contains; but it is wisely provided, that along with this nitrogen in all plants, a certainproportion of starch or sugar and of saline and earthy matter are always associated—so that the quantity of nitrogen may be considered as a rough practical index of the proportion of some of the important saline and earthy ingredients also.
An important practical lesson on this subject is taught us by the study of the wise provisions of Nature. Not only does the milk of the mother contain all the elements of a nutritive food mixed up together—as the egg does also for the unhatched bird—but in rich natural pastures the same mixture uniformly occurs. Hence, in cropping the mixed herbage, the animal introduces into its stomach portions of various plants—some abounding more in starch or sugar, some more in gluten or albumen, some naturally richer in saline, others in earthy constituents; and out of these varied materials the digestive organs select a due proportion of each, and reject the rest. Wherever a pasture becomes usurped by one or two grasses—either animals cease to thrive upon it, or they must crop a much larger quantity of food to supply the natural waste ofallthe parts of their bodies.
It may indeed be assumed as almost a general principle, that wheneveranimals are fed on one kind of vegetable only, there is a waste of one or other of the necessary elements of animal food, and that the great lesson on this subject taught us by nature is, that, by a judicious admixture, not only is food economised, but the labour imposed upon the digestive organs is also materially diminished.
In this little work, now brought to a close, I have presented the reader with a slight, and I hope plain and familiar, sketch of the various topics connected with practical agriculture, on which the sciences of chemistry and geology are fitted to throw the greatest light.
We have studied the general characters of the organic and inorganic elements of which the parts of plants are made up, and the several compounds of these elements which are of the greatest importance in the vegetable kingdom. We have examined the nature of the seed,—seen by what beautiful provision it is fed during its early germination—in what form the elements by which it is nourished are introduced into the circulation of the young plant when the functions of the seed aredischarged,—and how earth, air, and water are all made to minister to its after-growth. We have considered the various chemical changes which take place within the growing plant, during the formation of its woody stem, the blossoming of its flower, and the ripening of its seed or fruit,—and have traced the further changes it undergoes, when, the functions of its short life being discharged, it hastens to serve other purposes, by mingling with the soil, and supplying food to new races. The soils themselves in which plants grow, their nature, their origin, the causes of their diversity in mineral character, and in natural productiveness, have each occupied a share of our attention—while the various means of improving their agricultural value by manuring or otherwise, have been practically considered, and theoretically explained. Lastly, we have glanced at the comparative worth of the various products of the land, as food for man or other animals, and have briefly illustrated the principles upon which the feeding of animals and the relative nutritive powers of the vegetables on which they live are known to depend.
In this short and familiar treatise I have not sought so much tosatisfythe demands of the philosophical agriculturist, as toawakenthe curiosity of my less instructed reader, to shew him how much interesting as well as practically useful information chemistry and geology are able and willing to impart to him, and thus to allure him in quest of further knowledge and more accurate details to my larger work,[27]of which the present exhibits only a brief outline.
J. P. Wright, Printer, 18 New street, N. Y.